Effects Of Pyraclostrobin On The Soil Microorganisms In Wheat And Maize Continuous Cropping System

Pyraclostrobin is a strobilurin fungicide that has a broader antifungal activity spectrum and higher efficiency and security profiles than do previously used fungicides.The amount of pyraclostrobin used is enormous.At present,most of the toxicological studies on pyraclostrobin are carried out in the laboratory and the research that focused on the adverse effects of pyraclostrobin in field application has not been reported.Wheat and maize are important food crops and economic crops.Pyraclostrobin can prevent and control diseases on wheat and maize.However,during spraying,pyraclostrobin inevitably remain in the soil,which will affect the soil ecosystem.Therefore,it is necessary to study the ecotoxicological effects of pyraclostrobin on wheat and maize fields.In 2017 and 2018,the recommended dose(150 g/hm~2 in wheat field,187.5 g/hm~2 in maize field)and double doses(300 g/hm~2 in wheat field,375 g/hm~2 in maize field)were used in the occurrence period of wheat and maize diseases.In 2017,the spraying date of wheat field was April 22,and the spraying date of maize field was July 12.In 2018,the spraying date of wheat field is April 15,and the spraying date of maize field is July 17.We regularly collected soil samples,and measured the quantity of soil bacteria,fungi and actinomyces by using dilution coating plate counting method,measured the activities of alkaline phosphatase,?-glycosidase,urease and dehydrogenase by using traditional soil enzyme assay method,measured the expression level of AOA-amo A and AOB-amo A by RT-PCR technology.What is more,16S r DNA high-throughput sequencing technology has been applied to determine the changes of soil bacterial community structure.The specific results are as follows:(1)In the two-year experiment,pyraclostrobin could significantly inhibit bacteria and fungi in wheat and maize fields after pyraclostrobin was applied to the corresponding crop at the recommended dose and double doses.Pyraclostrobin also could affect actinomycetes in the two-year experiment.But the effect of pyraclostrobin on actinomycetes was not similar in each experiment,which may be caused by the joint action of environmental factor and pyraclostrobin.(2)In the two-year field experiment,pyraclostrobin could affect the four soil enzymes after pyraclostrobin was applied to the corresponding crop at the recommended dose and double doses.Due to the complex and diverse field conditions,the changes of the soil enzyme activity were different in the two-year field experiment.On the whole,alkaline phosphatase activity in the treatment group was activated in the2017 year's wheat field and maize field experiments.However,the alkaline phosphatase activity in the treatment group was inhibited in the wheat field experiment in 2018.In the maize field experiment in 2018,the alkaline phosphatase activity in the treatment group was first activated and then recovered to the control level.During the wheat field experiment in 2017,the activity of?-glycosidase in the treatment group was activated.In the 2018 year's wheat field experiment,the activity of?-glycosidase in the treatment group was not inhibited on day 1 and was inhibited on days 14 and 51.On the whole,?-glycosidase activity in the treatment group was inhibited during the two-year maize field experiment.In the two-year wheat field experiment,except for individual treatments in individual cycles,the urease activity in the treatment group was inhibited.On the whole,the urease activity in the treatment group was similar to the control level in the 2017 year's maize field experiment.In the 2018 year's maize field experiment,the urease activity in the treatment group was firstly inhibited and then restored to the control level.Pyraclostrobin also could affect the dehydrogenase activities in wheat and maize fields.However,during the two-year experiment,the changes of dehydrogenase activity were inconsistent after pyraclostrobin was sprayed in each season crop.(3)In the two years'wheat field experiment,pyraclostrobin could significantly inhibit the expression level of AOA-amo A gene.On the whole,the AOA-amo A gene expression in the treatment group was higher than that in the control group in the 2017 year's maize field experiment.In the 2018 year's maize field experiment,except for the AOA-amo A gene expression level in the treatment group on day 14,the expression level of AOA-amo A gene in the treatment group was higher than that in the control group in the other periods.In the 2017 year's wheat field experiment,only on day 48,the expression level of AOB-amo A gene in each treatment group was significantly lower than that in the control group.In the 2017 year's maize field experiment,the expression level of AOB-amo A in the treatment group didn't show a significant trend of inhibition.However,in the 2018 year's wheat and maize field experiments,the expression level of AOB-amo A gene in the treatment group showed a significant trend of inhibition.(4)In the two-year field experiment,after pyraclostrobin was applied to the corresponding crop at the recommended dose and double doses,pyraclostrobin could significantly affect the bacterial community,and there was a cumulative effect.In addition,after the pyraclostrobin was applied in the two-year field experiment,it ccould be found that the common stable dominant phyla in wheat and maize fields were Proteobacteria,Acidobacteria,Bacteroidetes,Actinobacteria and Gemmatimonadetes,the common stable dominant bacteria genera were Sphingomonas,Gemmatimonas,Gp4 and Gp6.In general,pyraclostrobin may cause a serious impact on the circulation of N and P elements in soil and degradation of hydrocarbon and other organic pollutants.(5)After pyraclostrobin was applied to the corresponding crop at the recommended dose and double doses,no significant dose-effect relationship was found in studies of the effects of pyraclostrobin on above indexes.The ecological toxicity of pyraclostrobin to the soil microorganisms in the actual environment was studied from different perspectives using above biomarkers,which can provide data support for the ecological risk assessment of pyraclostrobin.